Coffee houses have been a part of the “coffee culture” since the 17th century. Throughout the years methods of making coffee have been refined and skilled people trained to produce the best coffee beverages. The first coffee machines were developed in the early 1800s and an automatic espresso machine was invented in the 1930s. The automation of the coffee making process has, in turn, lead to a rapid growth, particularly in the last ten years, in the number of coffee houses/shops with more specialist drinks, such as espresso and cappuccino, being in high demand. These types of beverages have historically been regarded as luxury items because of the need for expensive, complex machines capable of producing the high pressures necessary for making them, which had to be properly operated and maintained by a trained barista to produce good quality. Coffee aficionados agree that an espresso can be spoiled by a badly trained operator despite the use of a good quality machine and good quality coffee. This trend, however, has not only lead to an increased demand from consumers for luxury top quality beverages, but also a desire for a greater variety of specialty beverages, and the ability to make such beverages in the comfort of one's own home.
Although there is no agreed technical definition, it is generally understood that, compared to drip coffee, barista quality espresso has a thicker consistency, due to a higher amount of dissolved solids and fine oil droplets suspended throughout the drink. It has a smooth, yet thick, dark reddish brown crema making up 10 to 30% of the beverage. The crema is a polyphasic emulsion of air and the oils, proteins and sugars extracted from the coffee which is produced at a high pressure, traditionally in the region of 9 to 10 bar. The higher pressures increase the rate of coffee wetting and improve extraction as well as being responsible for the development of the crema. Air is entrained into the beverage as it is being brewed to produce the desired crema.
It is acknowledged, by discerning espresso drinkers, that espresso produced using water which is cooler than the optimum temperature tastes sour and that produced with water which is hotter than this temperature tastes bitter. The optimum temperature is claimed to be between 92 and 96° C. Other factors which affect the quality of the espresso include the roasting and age of the coffee beans, the grind size, the compaction of the grinds prior to brewing, and the brew time. The “best” espresso is achieved by balancing these key elements of the brewing process.
Domestic coffee machines have also developed significantly since the first filter machines were invented in the 1960s and coffee machines are now essential pieces of kitchen equipment in many households. Some such machines dispense individual servings of a beverage directly into a drinking receptacle, and derive the beverage from a bulk supply of beverage ingredients or from individual packages of beverage ingredients such as pods, pads or cartridges. In the following specification such packages will be referenced by the general term cartridges. Machines that use such cartridges require far less cleaning and can enable the user to make a selection of beverages. The beverages are formed from brewing, mixing, dissolving or suspending the beverage ingredients in water. For example, for coffee beverages, heated water is forced through the cartridge to form the extracted solution. The cartridge may be designed so that air becomes entrained so as to produce a desired foam or crema. The extracted solution passes along a conduit to an outlet nozzle provided at a dispensing station. The dispensing station comprises a stand upon which a receptacle may be supported. The outlet nozzle is positioned above the stand such that the beverage is dispensed through the outlet nozzle and into the receptacle. Cleaning may be performed using a steam purge, i.e. passing steam through the conduit. The use of cartridges in domestic coffee machines has become increasingly popular due to their convenience and the quality of the beverage produced. An example of a machine for preparing beverages using cartridges is described in EP-A-1440644, and examples of cartridges are described in EP-A-1440903.